To produce high-quality steel, the carbon content (C) of the starting raw material has to be reduced. The starting raw material can in this case partly be obtained from scrap which is firstly melted in an apparatus, for instance a converter or an electric arc furnace, and then decarburized. To carry out the decarburization, oxygen (O2) is blown into the melt and oxidizes the carbon present in the melt. The carbon monoxide (CO) produced in this way forms gas bubbles in the melt and these rise to the surface of the latter and pass through the slag on the surface of the melt. In a gas space above the melt, carbon monoxide can be partly oxidized to carbon dioxide or completely oxidized by means of after-combustion devices. An offgas containing CO, CO2 and also H2, H2O and N2 leaves the apparatus through an offgas outlet and primary gas is generally passed to a dust removal plant and a filter plant.
However, the formation profile of CO is not always proportional to the amount of oxygen blown in, which is attributable to the fact that the liquid melt is able, depending on the flow and temperature situation, to dissolve and retain the resulting CO in a metastable fashion. Sometimes there is no longer the necessary impulse for the CO gas collected in the melt to rise and the critical point at which the gas rises is reached only at an appropriate gas bubble size or induced only by secondary influences, e.g. flushing elements. The gas is then given off quite suddenly. This undesirable effect, known as boiling, can lead to a safety hazard and material damage to the apparatus and associated peripherals, for instance dust removal from the primary gas or a filter plant.